Periodic Lateralized Epileptiform Discharges Research Articles

Similarity of Lateralized Rhythmic Delta Activity to Periodic Lateralized Epileptiform Discharges in Critically Ill Patients

The increasing use of continuous electroencephalography (EEG) monitoring in the intensive care unit has led to recognition of new EEG patterns that are of unclear or unknown significance. To describe an EEG pattern, lateralized rhythmic delta activity (LRDA), encountered in critically ill subjects and determine its clinical significance in this setting. DESIGN, SETTING, AND PARTICIPANTS Retrospective review at an academic medical center of EEG recordings, medical records, and imaging studies of critically ill patients with LRDA and comparison with subjects with lateralized periodic discharges (also known as periodic lateralized epileptiform discharges), subjects with focal nonrhythmic slowing, and controls. Electroencephalography or continuous electroencephalography. Cross-sectional prevalence of lateralized rhythmic delta activity; EEG characteristics; etiology, clinical, and radiological correlates; and risk of early seizures. We identified LRDA in 4.7%of acutely ill subjects undergoing EEG or continuous EEG monitoring. It was often associated with other focal EEG abnormalities, including lateralized periodic discharges in 44%of cases. The most common conditions associated with LRDA were intracranial hemorrhage and subarachnoid hemorrhage. Lateralized rhythmic delta activity was an independent predictor of acute seizures, with 63%of subjects having seizures during their acute illness, a proportion similar to subjects with lateralized periodic discharges (57%) and significantly higher than associated with focal nonrhythmic slowing (20%) or in control subjects (16%). Most patients (80%-90%) in the LRDA and lateralized periodic discharges groups who had seizures while undergoing continuous EEG monitoring had only nonconvulsive seizures, whereas this was the case for only 17%of patients in the other groups. Lateralized rhythmic delta activity and lateralized periodic discharges were both associated with lesions involving the cortex or juxtacortical white matter. Lateralized rhythmic delta activity in critically ill patients has a similar clinical significance as lateralized periodic discharges. It reflects the presence of a focal lesion and is associated with a high risk of acute seizures, especially nonconvulsive.

Spectrum of Nonconvulsive Status Epilepticus in Patients With Cancer

Determine incidence, clinical presentation, electrographic correlates, and outcome of nonconvulsive status epilepticus (NCSE) in cancer patients on whom an EEG was performed. Retrospective review of 947 EEG reports on 658 patients in whom any type of EEG was performed at Memorial Sloan-Kettering Cancer Center (July 2006 to March 2008). Using the Epilepsy Research Foundation criteria, patients were classified as definite or probable NCSE. Medical records were reviewed for diagnosis, causes of NCSE, response to treatment, and outcome. Mortality was determined for patients with NCSE. Twenty-six episodes of NCSE were identified in 25 patients (25/658, 4%). Eleven patients had primary brain tumor, 12 patients systemic cancer, and two had both. At diagnostic EEG, 18 were awake, 3 were lethargic, and 5 patients were comatose. EEG revealed a seizure in 62% of the patients, periodic lateralized epileptiform discharges in 42%, and periodic epileptiform discharges in 7.7%. Neuroimaging revealed new intracranial pathology in 54% of the patients. Seventy-seven percent of the patients achieved control; 65% required ≥3 antiepileptic drugs, and 33% required intubation. Three patients died from NCSE. In our cohort, awake NCSE was more common than comatose NCSE. Treatment was successful in patients with heterogeneous central nervous system disease. EEG evaluation should be considered in patients with cancer because NCSE is treatable despite a high prevalence of structural brain disease. Nonconvulsive status epilepticus control did not always require intubation and burst suppression, but frequently required three or more antiepileptic drugs.

Continuous EEG predictors of outcome in patients with altered sensorium

PurposeTo evaluate EEG predictors of outcome in patients with altered sensorium suspected to have seizure and to assess whether short term EEG is as effective as long term continuous EEG (cEEG) in predicting the outcome of patients with altered sensorium due to neurological causes. MethodsWe identified 99 consecutive critically ill patients with altered sensorium in whom nonconvulsive seizures were suspected. They underwent cEEG. Functional outcome was assessed with the modified Rankin Scale (mRS) at 4 weeks, discharge or death. We compared efficacy of short term EEG and long term continuous EEG in recording the abnormal patterns on EEG. Logistic regression analysis was performed to identify EEG findings associated with poor outcome, defined as mRS 4–6 (dead or moderately to severely disabled). ResultsPoor outcome was associated with nonconvulsive seizures (NCS), nonconvulsive status epilepticus (NCSE), periodic lateralized epileptiform discharges (PLEDS), PLEDS plus, generalized periodic epileptiform discharges (GPEDS) and abnormal EEG background. Short term EEG can detect seizure activity and other electrographic markers of poor outcome but the values are statistically insignificant. ConclusioncEEG monitoring provides independent prognostic information in patients with altered sensorium and suspected seizures. Unfavorable findings include nonconvulsive seizures, periodic epileptiform discharges and abnormal background. Short term EEG is ineffective in detecting seizures on EEG in patients with altered sensorium and should not be used as substitute for Long term EEG

Temporal Lobe Meningioma With Ipsilateral Herpes Simplex Encephalitis

An 87-year-old woman presented with subacute onset of headache, fever, and episodes of aphasia, eventually progressing to coma. Magnetic resonance imaging (MRI) revealed a newly identified enhancing left sphenoid wing meningioma with peritumoral edema in the underlying brain (Figure 1). MRI also demonstrated expansile fluid-attenuated inversion recovery (FLAIR) signal, restricted diffusion, and elevated plasma volume in the medial temporal lobe more suggestive of superimposed infection. Electroencephalogram (EEG) showed left periodic lateralized epileptiform discharges (PLEDS). Cerebrospinal fluid (CSF) analysis showed herpes simplex virus 1 (HSV1) by polymerase chain reaction (PCR). Despite treatment with intravenous acyclovir, the patient remained comatose and comfort measures were pursued. Herpes encephalitis has been described in the setting of cancer and brain metastases but not concurrently with meningioma.1,2 Postmortem examination confirmed HSV1 and meningioma (Figure 2). Figure 1. MRI showing an enhancing left sphenoid wing meningioma with edema in the underlying temporal lobe (white arrowheads in A, B), expansile FLAIR signal, restricted diffusion (red arrowheads in C, D), and elevated plasma volume in the medial temporal lobe ... Figure 2. Postmortem examination demonstrating herpes encephalitis and meningioma in situ (white arrow), as well as hemorrhagic necrosis of the left insula and medial temporal lobe (red arrowheads).

Prolonged ictal monoparesis with parietal Periodic Lateralised Epileptiform Discharges (PLEDs)

We report a patient with prolonged monoparesis and parietal periodic lateralised epileptiform discharges (PLEDs). The patient was a 73-year-old man with chronic myelomonocytic leukaemia who developed persisting monoparesis of the right arm, sensory aphasia, and finger agnosia, initially associated with focal clonic seizures. These neurological deficits remained for seven days without subsequent focal clonic seizures. The EEG showed left-sided PLEDs, maximal in the left occipito-parietal area. Ten days later, following phenytoin treatment, these symptoms suddenly improved and parietal PLEDs disappeared. Sustained PLEDs in the left parietal region may have been causally associated with ictal paresis in this patient.

A Case of Schizencephaly Has a Normal Surface EEG but Abnormal Intracranial EEG

Schizencephaly is a congenital malformation of the cerebral hemispheres, with communication between the lateral ventricle and the subarachnoid space. Marinelli reported that schizencephaly may be associated with continuous involuntary hand movements, such as dystonia or epilepsia partialis continua (EPC). We describe a young Chinese patient with continuous involuntary movements of the contralateral hand affected by schizencephaly. He has a normal scalp electroencephalogram (EEG) but abnormal intracranial EEG, with synchronized periodic lateralized epileptiform discharges. The results obtained from these EEG investigations and the clinical features of the involuntary movements are in favor of a diagnosis of secondary EPC.

Higher mortality rate is associated with advanced age and periodic lateralized epileptiform discharges in patients with refractory status epilepticus

To evaluate clinical data, electroencephalogram, etiology, classification, treatment, morbidity, and mortality in acute refractory status epilepticus. Fifteen patients, mean age of 41.3 years-old, six males, with refractory status epilepticus, were retrospectively studied. All of them were followed by serial electroencephalogram or continuous electroencephalographic monitoring. The most common comorbidity was hypertension. Seven (46.7%) patients were diagnosed with previous symptomatic focal epilepsy. More than one etiology was identified in 40.0% of the cases. Status epilepticus partial complex was the most common (n=14, 93.3%), and discrete seizures were the most observed initial ictal pattern. Continuous intravenous midazolam was used in nine (60.0%) patients and continuous thiopental in three (20.0%). Nine (60.0%) participants died, one (6.6%) had neurological sequelae, and five (33.3%) presented no neurological sequelae. Higher mortality rate was associated with advanced age and periodic lateralized epileptiform discharges. Midazolam proved to be a safe drug. The refractory status epilepticus is related to high mortality.

Sporadic Creutzfeldt-Jakob disease with focal findings: caveats to current diagnostic criteria

The clinical diagnosis of Creutzfeldt-Jakob disease (CJD) is largely based on the 1998 World Health Organization diagnostic criteria. Unfortunately, rigid compliance with these criteria may result in failure to recognize sporadic CJD (sCJD), especially early in its course when focal findings predominate and traditional red flags are not yet present. A 61-year-old man presented with a 3-week history of epilepsia partialis continua (jerking of the left upper extremity) and a 2-week history of forgetfulness and left hemiparesis; left hemisensory neglect was also detected on admission. Repeated brain magnetic resonance imaging (MRI) showed areas of restricted diffusion in the cerebral cortex, initially on the right but later spreading to the left. Electroence-phalography (EEG) on hospital days 7, 10, and 14 showed right-sided periodic lateralized epileptiform discharges. On day 20, the EEG showed periodic sharp wave complexes leading to a diagnosis of probable sCJD and subsequently to definite sCJD with brain biopsy. Neurological decline was relatively fast with generalized myoclonus and akinetic mutism developing within 7 weeks from the onset of illness. CJD was not immediately recognized because of the patient's focal/lateralized manifestations. Focal/lateralized clinical, EEG, and MRI findings are not uncommon in sCJD and EEG/MRI results may not be diagnostic in the early stages of sCJD. Familiarity with these caveats and with the most current criteria for diagnosing probable sCJD (University of California San Francisco 2007, MRI-CJD Consortium 2009) will enhance the ability to recognize sCJD and implement early safety measures.

Abstract TP122: Identifying Predictors of Seizure Recurrence After Nonconvulsive Seizures Recorded on Continuous Electroencephalogram (cEEG) in Ischemic Stroke

INTRODUCTION: Seizures are well-recognized complications of ischemic strokes (IS). The risk of subsequent development of epilepsy has been shown to be 2-4% in acute IS and much higher in remote IS. However, the risk of epilepsy in IS who have nonconvulsive seizures on cEEG is not well characterized. We present here a five-year retrospective study of IS patients who have nonconvulsive seizures on cEEG identifying risk factors for the development of epilepsy. METHODS: We retrospectively reviewed prospectively collected cEEG and clinical data on consecutive patients monitored from January 1, 2007, to December 31, 2011. We identified those patients with cEEG seizures that were secondary to either acute (<30 days) or remote (>30 days) ischemic stroke (IS; n=109) and then included in this study only those patients with follow-up encounters. Statistical analyses were performed with JMP 9.0. RESULTS: Sixty-five (41.5% acute IS, 58.5% remote IS) patients met inclusion criteria for this study. All patients were discharged on at least one antiepileptic. Nineteen (29.2%) patients were found to have seizure recurrence (i.e., epilepsy) with 84.2% being remote IS (p=0.0116). Periodic lateralized epileptiform discharges (PLEDs) were seen on cEEG in 21.5% (22.2% acute IS, 21.1% remote IS). 15.8% with PLEDs on initial cEEG developed epilepsy (p=0.74). 33.3% of patients classified as stupor/coma at the time of nonconvulsive seizures were found to have seizure recurrence compared to 24.1% of patients classified as awake/lethargy (p=0.5841). On follow up EEG (mean (SEM) 384.4 (59.1) days), the finding of sharp wave/spike (12.1%) significantly correlated with seizure recurrence (p=0.0175). DISCUSSION: This retrospective study found that patients with remote IS are at a higher risk of developing epilepsy when nonconvulsive seizures are recorded on cEEG in the hospital. Additionally, the finding of sharp waves on follow-up routine EEG further identifies those at risk for recurrence. This study highlights the usefulness of cEEG in patients in patients with acute or remote strokes and provides guidance on utility of follow-up EEG.

Periodic lateralized epileptiform discharges (PLEDs) in cerebral lupus correlated with white-matter lesions in brain MRI and reduced cerebral blood flow in SPECT

This is a case report on an uncommon correlation between periodic lateralized epileptiform discharges (PLEDs) and white-matter lesions in cerebral lupus, and with a reduced cerebral blood flow (CBF) in single-photon emission computed tomography (SPECT). A 47-year-old woman with a long-term history of systemic lupus erythematosus (SLE) presented with a seizure followed by frontal lobe dysfunction clinically. An electroencephalogram (EEG) showed bilateral independent PLEDs in the frontal region. A magnetic resonance image of the brain showed white-matter changes in the frontal periventricular region. Cerebral angiogram did not reveal any evidence of vasculitis. A cerebral SPECT with tracer injected during the EEG showing PLEDs showed a reduction in CBF in the frontal regions. Clinical recovery was observed with intravenous immunoglobulin. This case shows that PLEDs can be seen with white-matter changes in SLE.

Encefalitis por el virus de Epstein-Barr: descripción de un caso clínico y revisión de la bibliografía

INTRODUCTION. Infection by the Epstein-Barr virus (EBV) -either as a primary infection, a reactivation or an active chronic infection- can give rise to several clinical forms of involvement of the central nervous system. We report a case of encephalitis due to EBV produced by viral reactivation in an immunocompetent patient which initially mimicked, from the clinical and electroencephalographic point of view, encephalitis due to type 1 herpes simplex virus (HSV-1). CASE REPORT. A 51-year-old male who had reported the presence of dorsal herpes zoster some days earlier. The patient visited the emergency department after suffering a holocranial oppressive headache and febricula for seven days; 24 hours before admission to hospital, he was suffering from drowsiness and language disorder. The neurological examination revealed stiffness in the back of the neck and dysphasia. An analysis of the cerebrospinal fluid revealed pleocytosis (422 cells/mm(3)) with 98% of mononuclear cells and normal protein and glucose concentration levels in cerebrospinal fluid. Magnetic resonance imaging of the brain and electroencephalogram readings were normal with periodic lateralised epileptiform discharges in the left temporal region. Intravenous acyclovir treatment was initiated, but renal failure meant it had to be changed to oral valaciclovir with clinical resolution and improvement of the liquoral parameters. Polymerase chain reaction in the cerebrospinal fluid was positive for EBV and negative for the other neurotropic viruses. In blood, the serology test for EBV with IgG was positive, while IgM and heterophile antibody tests were negative. CONCLUSIONS. EBV infection can give rise to acute disseminated encephalomyelitis or affect several locations in the central nervous system, especially the cerebellum. Clinical pictures mimicking HSV-1 are less frequent. When encephalitis is related to viral reactivation, precipitating factors can be detected, as in our case.

Adversive seizures associated with periodic lateralised epileptiform discharges (PLEDs) after left orbital contusion

We report a patient who presented with adversive seizures associated with periodic lateralised epileptiform discharges (PLEDs), a month after head trauma. The PLEDs predominantly involving the left frontal contacts became more frequent at the onset of adversive seizures during EEG. Brain MRI demonstrated a contusion scar in the left orbital cortex with reduced diffusion, not only around this orbital lesion but also in the ipsilateral anteromedial thalamus. Single photon emission computed tomography revealed focal cerebral hyperperfusion in the left medial orbitofrontal region, basal ganglia, and thalamus. The abnormal metabolism involving the thalamus and striatum could be associated with the ipsilateral orbital contusion and might have been caused by cortical-subcortical, trans-synaptic hyperactivity. Further studies are warranted to determine the role of subcortical structures in the generation of PLEDs and adversive seizures. [Published with video sequences].

Independent and symmetric seizures from parasagittal cortex: Is this a feature of profound hypoglycemia?

Two patients presented with severe hypoglycemia and parasagittal homotopic cerebral hemisphere injury. Days after the initial insult, bilateral, independent, periodic lateralized epileptiform discharges and frequent seizures emerged from the affected homotopic cerebral cortices in both patients. We speculate that synaptic rescaling and increased spontaneous discharges in isolated cerebral cortex may cause epileptogenesis in severe hypoglycemia. Bilateral but temporally independent parasagittal seizures could be a feature of severe hypoglycemia.

Prolonged ictal aphasia: A diagnosis to consider

Aphasia is a common symptom encountered by clinical neurologists. It is usually caused by strokes or lesions involving language regions of the brain, yet prolonged aphasia is rarely the sole manifestation of a simple partial status epilepticus. We report six patients, who suffered from prolonged ictal aphasia. All but one patient had a structural lesion in the left hemisphere, only three suffered from clinical seizures during or shortly prior to the aphasic episode. All patients had ictal patterns on the electroencephalogram (EEG), four of whom had periodic lateralized epileptiform discharges, and five showed frequent recurrent electrographic seizures during the aphasic state. The aphasia lasted several days in all patients, and it resolved after administration of antiepileptic drug treatment. In conclusion, prolonged ictal aphasia is a rare but important treatable cause of aphasia. Surface EEG recordings should be obtained in all patients with unexplained prolonged aphasia to diagnose this rare but treatable entity.

Refractory nonconvulsive status epilepticus in coma: analysis of the evolution of ictal patterns

Nonconvulsive status epilepticus (NCSE) is currently considered as one of the most frequent types of status epilepticus (SE). The objective of the present study was to identify the natural history of the electrographical evolution of refractory NCSE and to establish the relationship between ictal patterns and prognosis. We analyzed, retrospectively, 14 patients with loss of consciousness and NCSE. The ictal patterns were classified as discrete seizures (DS), merging seizures (MS), continuous ictal discharges (CID), continuous ictal discharges with flat periods (CID-F), and periodic lateralized epileptiform discharges (PLEDs). The ictal patterns were DS (n=7; 50.0%), PLEDs (n=3; 1.4%), CID (n=2; 14.3%), MS (n=1; 7.1%), and CID-F (n=1; 7.1%). NCSE electrographic findings are heterogeneous and do not follow a stereotyped sequence. PLEDs were related to a higher probability of neurological morbidity and mortality.

Long-term outcome and prognosis of patients with emergent periodic lateralized epileptiform discharges (ePLEDs)

PurposeEmergent EEG (eEEG) is an EEG performed on a non-elective basis upon request from a clinician for a seemingly emergency indication. Little is known about the long-term prognosis of patients with emergent periodic lateralized epileptiform discharges (ePLEDs). MethodsWe analyzed the EEG and clinical records of patients with ePLEDs from January 2002 to December 2008. ResultsOut of 1948 eEEGs, 79 (4%) patients had ePLEDs. Sixty-three patients had ePLEDs and 16 had eBiPLEDs (emergent bilateral periodic lateralized epileptiform discharges). The etiology of ePLEDs was CNS infection and inflammation (35.4%), stroke (32.9%), and metabolic encephalopathy (11.4%). Of the surviving 52 (65.8%) patients with ePLEDs, 34 (65.4%) had persistent seizures during a mean follow-up of 28 months (range 12–72 months). Seizure as the initial presentation was more commonly seen in children as compared to adults (64% versus 31%, p=0.005). CNS infection and inflammation were also seen more frequently in the pediatric age group (50% versus 27%, p=0.04). At follow-up, patients with eBiPLEDs had more seizures than patients with ePLEDs (87.5% versus 61.3%). ConclusionePLEDs is associated with significant morbidity and mortality. However, the etiology of ePLEDs and brain dysfunction will influence the long-term outcome. This information is invaluable for prognostication and underscores the importance of rigorous management of patients with ePLEDs.

Periodic Lateralized Epileptiform Discharges (PLEDs) and pneumococcal meningoencephalitis

Pneumococcal meningoencephalitis (PME) is a life-threatening condition of the central nervous system (CNS), and is often the result of a complicated upper airway infection. Periodic Lateralized Epileptiform Discharges (PLEDs) are a typical electroencephalographic (EEG) pattern found in some acutely acquired brain insults. Within the pediatric population they are frequently seen in association with herpetic encephalitis, a CNS infection with a high morbidity and mortality rate. We report the case of a 3-year-old girl with a bilateral ear infection who developed convulsions and coma. She had early PLEDs lateralized to the right on the EEG and microbiological criteria for Streptococcus pneumoniae infection. Concomitant herpetic encephalitis was ruled out. Intensive antibiotic and antiepileptic treatment resulted in a remarkable improvement, with the patient being able to resume her normal activities within months. To our knowledge, the association of PME and PLEDs has not been previously described in children. On the other hand, EEG has scarcely been used in the management of acute CNS infections. Hence, non-herpetic CNS encephalitis with potentially more favorable outcomes ought to be considered in the differential diagnosis of PLEDs. Continuous EEG monitoring should be considered in children with CNS infections presenting with altered sensorium, independent of the presence of seizures.

Electro-Clinical and Imaging Characteristics of Ictal Periodic Lateralized Epileptiform Discharges (PLEDs) during Continuous EEG (cEEG) Monitoring: A Retrospective Analysis of 10 Cases (S58.002)

Objective: To investigate EEG features, clinical semiologies, and neuroimaging findings in patients with ictal PLEDs. Background PLEDs are classically viewed as acute interictal phenomena associated with seizures. Less frequently, however, PLEDs may represent the sole EEG correlate during clinical seizure activity. Limited case reports describing such ictal PLEDs cannot comment on their frequency or common characteristics. We present here the first systematic case series on ictal PLEDs. Design/Methods: We identified all records containing PLEDs and ictal PLEDs from our cEEG archives, which included all adult ward and ICU patients undergoing prolonged EEG monitoring for non-elective indications between 2007 and 2011. PLEDs were considered ictal when they were reported as being clearly time-locked to clinical symptoms. Source EEGs were reviewed for confirmation. Results: A total of 1452 patients underwent cEEG monitoring. PLEDs were reported in 90 patients, with ictal PLEDs observed in 10 (11.1% of those with PLEDs; 0.7% overall). Eight patients with ictal PLEDs were male and two were female. Nine had motor epilepsia partialis continua (EPC) and one experienced repetitive, stereotyped sensory symptoms. In all 10 patients, PLEDs were maximal over either central, parietal, or frontal regions contralateral to the side of clinical symptoms. Eight patients had identifiable lesions involving sensorimotor cortex ipsilateral to the PLEDs. These underlying lesions were neoplastic (5), anoxic (1), post-traumatic (1), or vascular (1) in etiology. Conclusions: Ictal PLEDs were overall uncommon but occurred in 11% of patients with PLEDs on cEEG. The vast majority of patients in whom PLEDs were considered ictal experienced motor EPC. Most had lesions involving sensorimotor cortex and all had PLEDs maximal over the central, parietal, or frontal regions contralateral to their clinical symptoms. These findings raise important questions about the substrate for ictal PLEDs as well as the significance of isolated PLEDs occurring over non-eloquent cortex or without an obvious time-locked clinical correlate. Disclosure: Dr. Sen-Gupta has nothing to disclose. Dr. Schuele has received personal compensation for activities with UCB pharma and GlaxoSmithKline as a speaker. Dr. Macken has received personal compensation for activities with Cyberonics and Lundbeck Research USA, Inc. as a speaker. Dr. Macken has received research support from UCB Pharma. Dr. Gerard has nothing to disclose.

Transient periodic lateralised epileptiform discharges (PLEDs) following internal carotid artery stenting

Background. Periodic lateralised epileptiform discharges (PLEDs) are EEG patterns consisting of periodic or pseudoperiodic unilateral, focal or hemispheric epileptiform discharges at a rate of 1-2Hz. PLEDs may be triggered by acute brain injuries or systemic metabolic changes such as fever, hyperglycaemia or electrolyte imbalance and may result in disturbance of consciousness and/or neurological deficits. Case report. A 58-year-old female with a history of focal epilepsy and deep brain haematoma presented with acute change in awareness, associated with EEG evidence of PLEDs, three days after a left internal carotid artery stenting procedure. Clinical examination, laboratory testing and MRI were unchanged with respect to pre-stenting investigations. Conclusion. In this patient, PLEDs may have been triggered by local haemodynamic changes due to reperfusion after stenting in a previously damaged brain area.

Periodic electroencephalographic patterns: usefulness of definition and classification

identified a peri-odic and lateralized pattern, which they described as periodic lateralized epilepti-form discharges (PLEDs). The acronym encapsulates the essential characteristics of PLEDs, namely, wide distribution, polymorphism, one or more sharp components in a repeti-tive way (usually at the rate of one to two seconds), and localization over the hemisphere. Subsequent studies have described other variable periodic patterns as two independent PLED types in the same EEG (BIPLEDs), multifocal PLEDs, generalized periodic epileptiform dis-charges (GPEDs), and stimulus-induced rhythmic, periodic, or ictal discharges (SIRPIDs)